/* Copyright 2018 The TensorFlow Authors. All Rights Reserved.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
==============================================================================*/

#include "tensorflow/core/grappler/optimizers/shape_optimizer.h"

#include "absl/status/status.h"
#include "absl/strings/str_cat.h"
#include "tensorflow/core/framework/tensor.pb.h"
#include "tensorflow/core/framework/tensor_shape.pb.h"
#include "tensorflow/core/framework/types.h"
#include "tensorflow/core/grappler/grappler_item.h"
#include "tensorflow/core/grappler/mutable_graph_view.h"
#include "tensorflow/core/grappler/op_types.h"
#include "tensorflow/core/grappler/utils.h"
#include "tensorflow/core/grappler/utils/symbolic_shapes.h"
#include "tensorflow/core/lib/core/errors.h"

namespace tensorflow {
namespace grappler {

// This optimizer first rewrites Prod(Shape(x)) into Size(x). It then uses
// symbolic shapes to simplify Div(Size(x), Size(y)) in the case that x and y
// share symbolic shapes that are unknown but known to be identical, e.g. we can
// deduce that Div(Size([2,?,2]) Size([1,?,2])) is 2 if the two unknown
// dimensions are known to be identical. This can be inferred if they share the
// same symbolic representation (negative integer dimension size).
Status ShapeOptimizer::Optimize(Cluster* cluster, const GrapplerItem& item,
                                GraphDef* optimized_graph) {
  // Do a quick check to determine if we can skip this optimizer.
  bool can_optimize = false;
  bool has_div = false;
  bool has_size = false;
  bool has_shape = false;
  bool has_prod = false;
  auto is_int = [](const NodeDef& node) -> bool {
    return node.attr().at("T").type() == DT_INT32 ||
           node.attr().at("T").type() == DT_INT64;
  };
  for (const NodeDef& node : item.graph.node()) {
    if (IsShape(node)) {
      has_shape = true;
    } else if (IsProd(node) && is_int(node)) {
      has_prod = true;
    } else if (IsDiv(node) && is_int(node)) {
      has_div = true;
    } else if (IsSize(node)) {
      has_size = true;
    }
    if ((has_shape && has_prod) || (has_div && has_size)) {
      can_optimize = true;
      break;
    }
  }
  if (!can_optimize) {
    return absl::AbortedError("Nothing to do.");
  }

  *optimized_graph = item.graph;
  GraphProperties properties(item);
  bool inferred_properties = false;
  {
    MutableGraphView graph(optimized_graph);
    // The product of all the dimensions in a tensor shape can be expressed more
    // simply as the size of the tensor.
    for (auto& node : *optimized_graph->mutable_node()) {
      if (!IsShape(node)) {
        continue;
      }
      for (MutableGraphView::InputPort fanout :
           graph.GetFanout(MutableGraphView::OutputPort(&node, 0))) {
        if (fanout.node->op() != "Prod") {
          continue;
        }
        if (fanout.node->attr().count("keep_dims") != 0 &&
            fanout.node->attr().at("keep_dims").b()) {
          // Keeping the reduced dimensions won't result in a scalar, so we
          // can't rewrite the whole expression directly as a Size operation.
          continue;
        }
        const MutableGraphView::OutputPort reduce_indices =
            graph.GetRegularFanin(MutableGraphView::InputPort(fanout.node, 1));
        if (!inferred_properties) {
          // Infer properties lazily in case they are not needed.
          TF_RETURN_IF_ERROR(
              properties.InferStatically(/*assume_valid_feeds=*/false,
                                         /*aggressive_shape_inference=*/false,
                                         /*include_tensor_values=*/false));
          inferred_properties = true;
        }
        const auto& prop =
            properties.GetOutputProperties(reduce_indices.node->name());
        const int prop_size = prop.size();
        if (prop_size <= reduce_indices.port_id) {
          continue;
        }
        const TensorShapeProto& reduction_indices_shape =
            prop[reduce_indices.port_id].shape();
        if (NumCoefficients(reduction_indices_shape) == 1) {
          const auto& input_props = properties.GetInputProperties(node.name());
          if (input_props.size() != 1) {
            continue;
          }
          // Rewrite the reduction of the shape dimensions as a Size operation.
          NodeDef size_node(*fanout.node);
          const DataType type = input_props[0].dtype();
          size_node.set_op("Size");
          size_node.set_input(0, node.input(0));
          size_node.set_input(1, AsControlDependency(node));
          size_node.mutable_attr()->erase("Tidx");
          size_node.mutable_attr()->erase("keep_dims");
          (*size_node.mutable_attr())["out_type"] = fanout.node->attr().at("T");
          (*size_node.mutable_attr())["T"].set_type(type);

          // The corresponding Size kernel might not exist on the device where
          // Prod was placed, so assign the Size kernel to the same device as
          // the input.
          size_node.set_device(node.device());

          // In the unlikely even that "Size" is not registered on the input
          // device, skip the optimization.
          Status s = IsKernelRegisteredForNode(size_node);
          if (!s.ok()) {
            continue;
          }

          fanout.node->Swap(&size_node);
        }
      }
    }
  }
  {
    MutableGraphView graph(optimized_graph);
    for (auto& node : *optimized_graph->mutable_node()) {
      // Try to convert the ratio of 2 symbolic tensor sizes into a constant.
      // This is possible whenever the symbolic dimensions in the numerator and
      // denominator cancel each other.
      if (node.op() == "Div") {
        const MutableGraphView::OutputPort input1 =
            graph.GetRegularFanin(MutableGraphView::InputPort(&node, 0));
        const MutableGraphView::OutputPort input2 =
            graph.GetRegularFanin(MutableGraphView::InputPort(&node, 1));
        if (input1.node == nullptr || input2.node == nullptr) continue;
        if (!IsSize(*input1.node) || !IsSize(*input2.node)) {
          continue;
        }
        if (!inferred_properties) {
          // Infer properties lazily in case they are not needed.
          TF_RETURN_IF_ERROR(
              properties.InferStatically(/*assume_valid_feeds=*/false,
                                         /*aggressive_shape_inference=*/false,
                                         /*include_tensor_values=*/false));
          inferred_properties = true;
        }
        const auto& prop1 = properties.GetInputProperties(input1.node->name());
        const auto& prop2 = properties.GetInputProperties(input2.node->name());
        if (prop1.size() != 1 || prop2.size() != 1) {
          continue;
        }
        const TensorShapeProto& shape1 = prop1[0].shape();
        const TensorShapeProto& shape2 = prop2[0].shape();
        int64_t result = ComputeSizeRatio(shape1, shape2);
        if (result >= 0) {
          // Replace div with constant.
          node.set_op("Const");
          DataType dtype = node.attr().at("T").type();
          node.mutable_attr()->erase("T");
          (*node.mutable_attr())["dtype"].set_type(dtype);
          TensorProto* t = (*node.mutable_attr())["value"].mutable_tensor();
          t->set_dtype(dtype);
          *t->mutable_tensor_shape() = TensorShapeProto();
          if (dtype == DT_INT32) {
            t->add_int_val(result);
          } else {
            t->add_int64_val(result);
          }
          node.set_input(0, AsControlDependency(node.input(0)));
          node.set_input(1, AsControlDependency(node.input(1)));
        }
      }
    }
  }
  return OkStatus();
}

}  // end namespace grappler
}  // namespace tensorflow
